Fluids

ABSTRACT

New compositions of use as hydraulic fluids comprising a compound of general formula I:

a United States Patent 1191 Alcorn et a1.

11] 3,779,930 Dec. 18, 1973 1 FLUIDS [73] Assignee: Imperial Chemical Industries of Australia and New Zealand Limited, Melbourne, Victoria, Australia 22 Filed: May 26,197]

21 App1.No.: 147,231

[30] Foreign Application Priority Data Oct. 9, 1970 Australia 1507/70 Oct. 9, 1970 Australia 2813/70 [52] US. Cl. 252/77, 252/79 [51] Int. Cl C09k 3/00, C10m [58] Field of Search 252/73, 77, 76, 75, 252/79, 51.5 R, 56 S; 260/484 R, 465.6

[56] References Cited UNITED STATES PATENTS 2,942,033 6/1960 Leis et al. 252/404 X 2,200,495 5/1940 Fife 252/77 X 2,520,612 8/1950 Roberts et a1. 252/73 X 2,886,600 5/1959 Horsley et a1 252/73 X 2,998,389 8/1961 White 252/73 3,137,737 6/1964 Emrick et a1. 252/73 X 3,538,003 11/1970 Lothar 252/77 3,623,987 11/1971 Ker et a1 252/79 2,836,613 5/1958 Heininger..... 252/51.5 R X 2,226,599 12/1940 Zellhoefer.... 260/484 R 2,350,964 6/1944 Loder et a1. 260/484 R 3,278,585 10/1966 Baker et a1. 252/79 X FORElGN PATENTS OR APPLICATIONS 1,188,825 4/1970 Great Britain Primary ExaminerLeon D. Rosdol Assistant Examiner-Harris A. Pitlick Attorney-Cushman, Darby & Cushman [57] ABSTRACT New compositions of use as hydraulic fluids comprising a compound of general formula I:

R,(O Alk), CR

wherein Alk is an alkylene or aralkylene group containing from 1 to 9 inclusive carbon atoms in a straight or branched chain, R and R separately, is an alkyl, substituted alkyl or aralkyl group containing from 1 to 10 inclusive carbon atoms in a straight or branched chain and n is an integer from 1 to 10 inclusive, said compound having a viscosity at 40 C. of less than 1800 centistokes; and at least one additive.

4 Claims, No Drawings FLUIDS This invention relates to hydraulic fluid.

Hydraulic fluids are used in many pressure transmission systems, for example, in hydraulic machinery such as hydraulic presses and rams, and the clutching and braking systems of vehicles. The pressure transmission systems must operate over a wide range of conditions and the hydraulic fluid, to be effective, must not attack the machinery and must also remain a free flowing liquid under the extremes of the external conditions encountered.

The hydraulic brake systems of vehicles such as, for example, motor cars and aeroplanes comprise both metal and rubber parts exposed to the liquid employed as the hydraulic fluid. It is necessary that the hydraulic fluid does not attack either the metal or the rubber parts of the brake system, either at ordinary temperatures or at the elevated temperatures such as those caused by prolonged application of the brakes. The hydraulic fluid must also be unaffected by the low temperatures found during cold weather or in the case of aeroplanes in high altitude flight. This means that the freezing point should be below those temperatures likely to be encountered under operating conditions, and in addition the viscosity of the fluid should not increase under these conditions to such an extent that the easy working of the brakes is hindered. It is also essentialthat the hydraulic fluidshould have a high boiling point so as to ensure that the hydraulic fluid will not vaporize and cause vapour locks under operating conditions. The hydraulic fluidshould also have a low rate of vaporization and also sufficient lubricating properties to lubricate the moving parts of the system.

Conventional hydraulic fluids normally comprise a major proportion of polyalkylene glycols, and/or polyalkylene glycol monoethers together with minor proportions of various additives.

In practice, it is found that hydraulic brake fluids based on polyalkylene glycols and/or polyalkylene glycol monoethers are hygroscopic and in the passage of time water is absorbed from the atmosphere and the boiling point steadily falls. It is not uncommon, for example, for a brake fluid, after several months service, to be found to contain about 1 percent of water and, on prolonged service, up to 3 percent of water may be found in such fluids.

It is important for a hydraulic brake fluid to retain a high boiling point throughout its useful life, since a reduction in boiling point may result in the formation of vapour locks with consequent failure of the braking system. So as to avoid this possibility, it is usual for current brake fluids based on polyalkylene glycols and/r polyalkylene glycol monoethers, to be changed at least once every two years, so that moisture is not allowed to accumulate in the hydraulic fluid. It is desirable that the boiling point of a fluid should not be allowed to fall below about 300F.

There is a need for hydraulic fluids of improved properties. In the past, hydraulic fluids for typical heavy duty braking systems had a boiling point of about 400F, but with generally increased severity of operation, especially in vehicles fitted with disc brakes, there is now a need for hydraulic fluids having even higher boiling points; and fluids boiling at a temperature greater than 500F. are desired.

We have now found that hydraulic fluids comprising certain diethers have the desirable properties of high boiling point, low freezing point, acceptable rubber swell, and low hygroscopicity.

Accordingly we provide a hydraulic fluid comprising at least one diether of general formula I:

R (O Alk) 0R wherein Alk is an alkylene or aralkylene group containing from 1 to 9 inclusive carbon atoms in a straight or branched chain, R, and R separately, is an alkyl, substituted alkyl or aralkyl group containing from I to 10 inclusive carbon atoms in a straight or branched chain and n is an integer from 1 to 10 inclusive, said diether having a viscosity of less than 1800 centistokes at 40C.; and at least one additive.

Satisfactory hydraulic fluids may be obtained, for example, when R, is alkyl, aralkyl, beta-cyanoalkyl or beta-alkoxycarbonylalkyl and R is beta-cyanoalkyl or beta-alkoxycarbonylalkyl.

Suitable diethers used in our invention may be prepared by known means from condensates of ethylene oxide, propylene oxide, butylene oxide, styrene oxide, alpha-methyl styrene oxide or mixtures thereof, with water or an alkyl or aralkyl alcohol containing from 1 to 10 inclusive carbon atoms. Among suitable condensates, there may be mentioned, for example, ethylene glycol, ethylene glycol monomethylether, ethylene glycol monoethyl ether, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, propylene glycol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol, dipropylene glycol monobutyl ether, dipropylene glycol monoethyl ether, tripropylene glycol, tripropylene glycol monomethyl ether and tripropylene glycol monoethyl ether.

We have found under certain circumstances that the use of a mixture of diethers in our hydraulic fluids is beneficial. Thus the inclusion of a proportion of diethers of formula I, wherein n is an integer from 20 to inclusive, in our hydraulic fluids improves the lubricating characteristics of our hydraulic fluids.

Particularly suitable hydraulic fluids may be prepared when R is a beta-cyanoalkyl group. Such a group may be introduced into the diethers used in our hydraulic fluid by reacting suitable condensates as illustrated above with beta-cyano-olefines such as for example acrylonitrile or methacrylonitrile.

Accordingly we provide a hydraulic fluid comprising a diether of general formula II:

R (O Alk) O CHR CHR, CN

wherein Alk is an alkylene or aralkylene group containing from 1 to 9 inclusive carbon atoms in a straight or branched chain, R is an alkyl, substituted alkyl or aralkyl group containing from 1 to 10 inclusive carbon atoms in a straight or branched chain, R and R separately, is a hydrogen atom or an alkyl group containing from 1 to 4 inclusive carbon atoms and n is an integer from 1 to 10 inclusive, said diether having a viscosity of less than l800 centistokes at 40C; and at least one additive.

The additives are selected from those known in the art to be effective for improving the properties of hyhaving a viscosity at 40C of 260 centistokes with 0.3 parts of Topanol A.

Hydraulic fluid D was prepared by mixing 997 parts of tripropylene glycolmethyl ether beta-methyl-betadraulic fluids. Hydraulic fluids normally contain 5 cyanoethyl ether having a viscosity at 40C. of 1570 amongst other ingredients various additives such as lucentistokes with 0.3 parts of Topanol A. bricating additives, corrosion inhibitors, antioxidants The total reflux boiling point, freezing point (nonand the like. The exact nature of the additives required stirrable) rubber swell and the water uptake of hydrauto obtain a hydraulic fluid of optimum performance he fluid A. B. C and D were measured. The water upmay be found by the meth d ll d b those take was measured in the following manner. A weighed skilled in the an, sample (5 g) of the hydraulic fluid was exposed, in a Lubricity additives which a b d i our shallow dish, in a humidity chamber under a constant tion include, for example, Ucon lubri ant (Trad atmosphere of 75 percent relative humidity at 75F. Mark for polyalkylene glycols), alkoxylated a t oil The samples were weighed after being kept under these or borate esters. Certain of the diethers described here- Conditions for 96 hours. The water uptake was the perinabove may also be used as lubricity additives. Corro- Cemage increase in Weight P Unit Weight of the g sion inhibitors which may be used in our invention inha] p clude, for example, heterocyclic nitrogen containing The rubber Swell was measured y measuring the compounds, amines or derivativ s f i organic crease of diameter in inches of the base of a styrene phosphates or certain inorganic salts known in the art. rubber Piston C P aft th Cup had n imm rsed in Certain compounds may be used both as corrosion ina hydraulic fluid at temperature of 120C for 70 hibitors and as lubricity additives, these include, for exhoursample, orthophosphate salts of primary or secondary The rubber cups used in this test were of a standard aromatic amines, dialkyl citrates, aliphatic dicarboxylic Size having a base diameter in the range cm to acids and es er her f, A i id hi h may b cm. inclusive. The results obtained are tabulated in used in our invention include, for example, diaryl Table amines, compounds of the class commonly known as TABLE 1 hindered phenols and heterocyclic compounds known in thC 8ft. Freezing The invention is illustrated but by no means limited Hydmw by the following examples in which all parts are parts lic boiling stirrahle) Water Rubber by weight unless otherwise stated Q 222" t: EXAMPLEI 2 22.: 2-22 '31.: 13-222 Hydraulic fluid A according to this invention was D 575 m (H03 repared by mixin 99.7 parts of l-(2-methoxyethoxy)- -(Z-cyanoethoxyf-ethane having a viscosity at 40C EXAMPLE 2 of 400 centistokes with 0.3 parts ofTopanol A (Trade A series of hydraulic fluids were prepared by mixing Mark of Imperial Chemical Industries Limited for 2- separately 99.7 parts of the compounds whose structert-butyl-6methyl-p-cresol). 4O ture is shown in Table 2 with 0.3 parts ofTopanol A. Comparative hydraulic fluid B not of our invention, The boiling point, water uptake, freezing point, and was prepared by mixing diethylene glycol monomethyl rubber swell of the compositions were measured and ether (99.7 parts) with Topanol A (0.3 parts). the results are shown in Table 2. The water uptake and Hydraulic fluid C was prepared by mixing 99.7 parts the rubber swell were measured by the method of Exof 1-(2-methoxyethoxy)-2-(2-cyanopropoxy)-ethane ample 1.

TABLE 2 Freezing Viscosity of Total reflux point (noncompound in boiling point stirrable) Wateruptake Rubber swell centistokes of hydraulic of hydraulic of hydraulic of hydraulic Structure of compound at 40C. fluid (F.) fluid (C.) flui fluid CH 1O(CH2)2OCH2-CH2CN 6L2 439 5.0 +0.027 CH,-,CH2OCH2CH2OCH2CH2CN 88.6 453 60 4,6 +.0l3 CH CH -O(CH CH O) CH CH CN 540 534 60 39 +027 E K H2CHZO)2CH2CH2 530 584 60 2.3 +079 CH3 207 533 72 3.9 +.O32 CH;,-OCH2CHOCHZCHZCN ;i 2 z ):.1CH2CH CN 910 550 60 8.6 +013 :i 2 2 zO):.1-CHzCH CN I190 560 57 7.6 +040 sured by the method of Example 1 was 0.029.

TABLE 2 (ominucd Freezing Viscosity of Total reflux point (noncompound in boiling point stirrable) Water uptake Rubber swell centistokes of hydraulic of hydraulic of hydraulic of hydraulic Structure of compound at 40C. fluid (F.) fluid (C.) fluid fluid CRT-4 H THCH,()--(I l-l,4Il-\l\ m i 120 A 456 65 "A" 33 +.160

C=O CH, OCH CH-O CH OCH CH O-CH CH 257 545 65 6.6 .073

C=O CH O-(CH CH,O-)

CH O(CH,CH,O) CH -Cl: 620 595 65 5.7 +.072

C=O CH .,O(CH,-CH

EXAMPLE 3 M EXAMPLE 8 7' v i A hydraulic fluid was prepared by mixing diethylene glycol methylether 2-cyanoethyl ether 80 parts) with Ucon 50 H3660 (20 parts) (Ucon 50 H8660 is a Trade Mark for polyalkylene glycols).

The hydraulic fluid was found to have a viscosity at 40C of 1640 centistokes and the rubber swell as measured in Example 1 was 0.018.

EXAMPLE 4 xxiim A hydraulic fluid was prepared by mixing diethyleneglycol 'methylether 2-cyanoethyl ether (60 parts), diethylene-glycol n-butylether 2-cyanoethyl ether parts) and Ucon 50 HB260 (20 parts).

The hydraulic fluid was' found to have a viscosity at 40C of 1090 centistokes and the rubber swell mea- 'EXKMP'LE 6 A hydraulic fluid was prepared by mixing diethyleneglycol methylether 2-cyanoethylether (50 parts) with propyleneglycol bis-2-cyanoethyl ether (50 parts).

The hydraulic fluid was found to have a viscosity at 40C of 1290 centistokes and the rubber swell measured by the method of Example 1 was 0.007.

EXAMPLE 7 A hydraulic fluid was prepared by mixing diethyle'neglycol ethylether 2-cyanoethylether (60 parts) with propyleneglycol bis-2-cyanoethyl ether (40 parts).

The hydraulic fluid was found to have a viscosity at 40C of 1500 centistokes and the rubber swell measured by the method of Example 1 was 0.012.

A hydraulic fluid was prepared by mixing diethyleneglycol methylether 2-cyanoethylether (79.7 parts) Ucon 50 H8660 (20 parts), Topanol A (0.3 parts) benzotriazole (0.02 parts), di-n-butylamine (0.30 parts) and m-dinitro-benzene (0.05 parts).

The hydraulic fluid was found to have the properties shown in Table 3.

TABLE 3 Total reflux boiling point 522F viscosity 1640 centistokes P 10.9 rubber swell 0.018 loss in weight by evaporation 72% at C The degree of rubber swell was measured by the method of Example 1.

The hydraulic fluid was found to have acceptably low corrosive action on tinned iron, steel, cast iron, brass, copper and aluminium.

We claim:

1. Ina method for transmitting pressure using a hydraulic fluid, the improvement wherein said hydraulic fluid consists essentially of one or more diethers of general formula:

whereinAlk is an alkylene group containing from 1 to 4 inclusive carbon atoms in a straight or branched chain, R is alkyl containing from 1 to 10 inclusive car- .bon atoms in a straight or branched chain, R is a betacyanoalkyl group containing from 1 to 10 inclusive carbon atoms and n is from 1 to 10 inclusive, said diether having a viscosity of less than 1800 centistokes at 40C.

2. A method according to claim 1 wherein the betacyanoalkyl R, is the group CHR CHR, CN wherein R and R are each selected from the group consisting of hydrogen and alkyl containing from 1 to 4 inclusive carbon atoms.

3. A method according to claim 2 wherein each of R and R separately, is hydrogen or methyl.

4. A method according to claim 1 wherein the diether is l-(2-methoxyethoxy) -2-(2-cyanoethoxy)-ethane.

, n ITED STATES PATENT OFFICE g CERTIFICATE OF CQRRECTEDN Patent: No. 3,779,930 pared December 18, 1973 Inventor) Percival George Ernest Alcorn 1; 1

It is certified that error appears in the above-identified patent and that said- Letters Patent are hereby corrected as shown below:

In the heading, the Foreigh A lication Priority data for Australian Application No. 1507/70 should read --June 16, 1970.

Signed and sealed this" 9th d ay'of July 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Pa-tents 

2. A method according to claim 1 wherein the beta-cyanoalkyl R2 is the group -CHR3 -CHR4 -CN wherein R3 and R4 are each selected from the group consisting of hydrogen and alkyl containing from 1 to 4 inclusive carbon atoms.
 3. A method according to claim 2 wherein each of R3 and R4, separately, is hydrogen or methyl.
 4. A method according to claim 1 wherein the diether is 1-(2-methoxyethoxy) -2-(2-cyanoethoxy)-ethane. 